avast doesn’t say that a infection is detected.
avast says that domain and/or IP is blocked/blacklisted.

Blacklistings on that ASN/IP :
http://urlquery.net/report.php?id=1496751620674

Name mismatch with certificate 2 :
https://www.ssllabs.com/ssltest/analyze.html?d=smokestak.co.uk&s=198.185.159.144&latest

Vulnerable library found :
http://retire.insecurity.today/#!/scan/8d9b02f8862b6972cc25c522b11c12ddeb4e80178a14473dcad60890540d568b

Really bad IP history :
https://www.virustotal.com/en/ip-address/198.185.159.144/information/

My advise :

  • Fix the vulnerable library problem
  • Fix the certificate mismatch
  • Get dedicated hosting